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FELINE DENTISTRY
FELINE MALOCCLUSION Peter Emily, DDS
Malocclusion may be defined as any variation or deviation from normal occlusion. In normal feline occlusion, the incisor and canine teeth are in a "scissor" relationship; that is, the incisal edges of the lower incisor teeth strike the cingulum of the upper incisor teeth. The lower canine teeth occlude mesial to the upper canine and distal to the upper lateral incisors. Ideally the lower canine is placed equidistant between the upper third incisor and the upper canine tooth. The lower third premolar is rostral to its upper counterpart, the third premolar. The lower fourth premolar is also rostral to the upper fourth premolar. The upper fourth premolar covers the lower first molar buccally from mesial to distal. The upper first molar may strike the distal occlusal surface of the lower first molar (Fig. 1). Problems associated with feline malocclusions often are due to the development of new breed head types with variable occlusal patterns that fail to conform to normal occlusal relationships. A harmonious correlation between the component parts is of utmost importance for the functional capacity and maintenance of health within the masticatory system. It was believed by early orthodontists that malocclusions in general were diseases of civilization and improper jaw function. With the development of genetic research, malocclusions were found to be the result of inherited dentofacial proportions that are altered by developmental variations, trauma, or altered function. 2 Specific bites or occlusal relationships result from years of established breeding within a family or breed. Although very little has been written about feline dental occlusion, there is now an increasing awareness of the need for treatment of feline malocclusions. Malocclusion results from disproportionate tooth size or from disproportionate length of upper jaw to lower jiJ.W. Small teeth and large jaws, or large maxilla and small mandible, or any combination of these may be inherited. These disproportions in size are rarely seen in the wild, thanks to survival of the fittest. Genetic isolation of species usually produces uniformity in occlusion, with disturbances in occlusion bred out and eliminated from the species. From Colorado State University College of Veterinary Medicine and Biomedical Sciences, Fort Collins, Colorado; and University of Missouri School of Veterinary Medicine, Columbia, Missouri VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 6 • NOVEMBER 1992
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M1
Figure 1. Normal occlusion.
Malocclusion as primarily a genetic problem was developed by breeding experiments with animals carried out in the 1930s. Experiments by Stockard involved the cross-breeding of dogs.' The results of these experiments apply to feline malocclusion. Stockard crossed dogs of diverse sizes and types to determine the effects on jaw and tooth size. Stockard's experiments indicated that dramatic malocclusions did occur as the result of cross-breeding. These same results are seen in breed type development in cats; for example, discrepancies from tooth size-jaw size imbalances. His experiments concluded that independent inheritance of facial characteristics could be a major cause of malocclusion. The frequency of clinically evident feline malocclusion has been increased by the development of exaggerated head types. With the development of both the brachycephalic and dolichocephalic head types, occlusal relationships and individual teeth can assume positions different from the norm. This is most often expressed in the canine teeth in the extreme brachycephalic breeds, often with craniofacial asymmetry and accompanying wry bite. In the extreme flatnosed brachycephalic types, wry malocclusion is now common. Although teeth other than the canines are often in incorrect position, it is the canine teeth that cause the mechanical effects that present as clinical problems (Figs. 2 and 3). The prevalence of malocclusion in cats has been poorly documented. One study in the United Kingdom reported the prevalence as 3. 9% in all breeds of cats, with an increased prevalence (13%) in the long-haired cats. This study did not specify the prevalence specifically in the brachycephalic and dolicho-
FELINE MALOCCLUSION
1455
Figure 2. Brachycephalic head type. Extraoral canine.
cephalic types. 1 My own subjective observations of the flat-nosed brachycephalic types suggest an approximately 50% incidence of wry malocclusion . It is possible to move teeth by mechanical means into a desired position in many instances. This does not treat the cause of the malocclusion. Such treatment is appropriate only if ethical constraints have been satisfied. ETHICAL CONSIDERATIONS
The continuance of malocclusal problems is largely a result of action by owners of show cats. The short (average 3 to 5 years) life in the show ring is
Figure 3. Brachycephalic head type. Lateral view.
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often followed by years of breeding for cats that have achieved high status in the show ring. In that time, many types of malocclusion could be transmitted genetically. Ethical treatment of both genetic and developmental problems in cats is greatly influenced by cat breed standards. Dental standards are somewhat different for feline dentition and bite relationships than in dogs. Strict limitations regarding dental treatment are rigidly mandated by the American Kennel Club. They rightly state that dogs to be exhibited in the show ring cannot have a dental fault disguised by orthodontics or cosmetics to improve o~ normalize the dog's appearance. Such a specimen could transfer the fault to their offspring, degrading the breed. Feline show regulations do not stress bite types as a fault or disqualification, only that teeth should not be visible when the mouth is closed. Modern feline show' breeding has followed two trends, by exaggeration of the normal feline maxillary/mandibular relationship . In the brachycephalic breeds, the micrognathic maxilla has reduced arch space with crowding of the dentition, often with the superimposed cranial asymmetry of wry malocclusion. Unilateral mandibular prognathism is a common complication; one lower canine is visible because it sits outside the lip when the mouth is closed. This often results in soft tissue trauma to the upper lip (see Figs. 2 and 3). The dolichocephalic types frequently present with upper or lower canine teeth tipped laterally (buccal version), again producing soft tissue trauma (Fig. 4). Ethical considerations should stress protection of the proper occlusal relationship through sound breeding principles. Disregard of sound breeding can result only in perpetuation of unfit specimens. It is the duty of the veterinarian, however, to provide for a trauma-free and comfortable occlusion; cats with malocclusions that are to be treated orthodontically should be neutered.
Figure 4. Dolichocephalic head type. Lateral view.
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TREATMENT Feline orthodontic problems are often difficult to correct mechanically. The small shallow confines of the mouth make placement of bands, arch wires, and ligatures difficult. The short straight-sided premolars and tight shearing action of the carnassials present additional problems for proper band and bracket placement. Because feline show regulations require only that the teeth are not visible when the mouth is closed, the most practical, successful, and trauma-free therapy for those teeth creating soft tissue trauma is extraction or coronal length reduction and vital pulpotomy (see the article on endodontics for pulpotomy procedure elsewhere in this issue). Vital pulpotomy takes the offending teeth out of contact with the soft tissue while maintaining tooth vitality. Mechanical movement of feline dentition is rarely needed for function. It is difficult to perfect, is traumatic, and is subject to repeated failure. Mechanical movement of prognathic extraoral mandibular canine teeth in labial version may be accomplished in the rare case in which there is need for it. Many types of tooth movement can be used . A simple cost-effective procedure uses hand-fashioned light ligature wire hooks secured to the labial surface of the canines with light bonded composite cement. The hooks are fashioned from 26-gauge wire using fine beak orthodontic pliers . For canine teeth that sit outside the lip when the mouth is closed (as seen in the wry malocclusions), a similar hook is secured to the lingual surface of the opposite lower first molar tooth because these canines usually need to be tipped lingually as well as distally. Buttons or hooks cannot be placed on the buccal surfaces of the lower first molar owing to the shearing action of the opposing upper fourth premolar against the buccal surface of the lower first molar. A light rubber ligature or power chain is placed between the canine and molar hooks. The cat usually tolerates the displacement of the tongue by the elastics or power chain fairly well (Fig. 5). Canine teeth in labial version as seen in the dolichocephalic breeds are moved similarly except the caudal hook is placed on the lingual surface of the
Figure 5. Wry malocclusion: Rubber power chain from extraoral canine to medial, lower, opposite first molar.
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A
Figure 6. A, Drawing, and 8, clinical view of labial prolusion of upper and lower canines. Rubber power chain from buccal to lingual lower; buccal to buccal upper.
Figure 7. Mandibular displacement resulting from poor fracture reduction .
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Figure 8. Vital pulpotomies to correct soft-tissue trauma shown in Figure 7.
lower first molar on the same side. For the upper canine tooth, the caudal button or hook is light-bonded to the buccal surfaces of the upper fourth premolar and the upper canine (Fig. 6). Obviously proper breeding principles are the ultimate corrective measures. Simple relief of soft tissue trauma through extraction or vital pulpotomy is the most ethical and practical therapy.
ACQUIRED MALOCCLUSION
Acquired malocclusion in cats is usually due to trauma or disease rather than produced by habitual behavior, as seen in humans. Trauma to developing permanent tooth buds, drift of permanent teeth owing to premature loss of primary teeth, and trauma to permanent teeth can lead to malocclusion. Primary teeth retained past their normal time of exfoliation, however, is not a common finding in cats. Traumatically induced malocclusion is usually the result of poor mandibular fracture reduction. This can result in mild to radical mandibular displacement with soft tissue damage produced by teeth out of alignment (Fig. 7). These teeth are best treated with vital pulpotomy to relieve tissue damage (Fig. 8). Mandibular symphyseal fractures are the most common type of fracture in cats and are comparatively easy to reduce; however, mandibular body fractures will result in malocclusion if improperly reduced. Temporomandibular joint fractures require special reduction or surgical intervention to avoid malocclusion. Mandibular luxation is usually the result of trauma, but genetically weak temporomandibular ligaments or attachments can cause subluxation and resulting malocclusion. Electric cord injury with gingival and osseous necrosis with tooth displacement can produce malocclusion. . Mass lesions either benign or neoplastic can result in malocclusion by mass displacement of the dentition.
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References 1. Crossley DA: J Br Vet Assn 1991 2. Proffit WR: Contemporary Orthodontics. St Louis, CV Mosby, 1989 3. Stockard CR: The genetic and endocrine basis for differences in form and behavior as elucidated by studies of contrasted pure-line dog breeds and hybrids. American Anatomical Memoirs. Philadelphia, Wistar Institute, 1941
Address reprint requests to Peter Emily, DDS 1051 Independence Street Lakewood, CO 80215
FELINE DENTISTRY
FELINE MALOCCLUSION Peter Emily, DDS
Malocclusion may be defined as any variation or deviation from normal occlusion. In normal feline occlusion, the incisor and canine teeth are in a "scissor" relationship; that is, the incisal edges of the lower incisor teeth strike the cingulum of the upper incisor teeth. The lower canine teeth occlude mesial to the upper canine and distal to the upper lateral incisors. Ideally the lower canine is placed equidistant between the upper third incisor and the upper canine tooth. The lower third premolar is rostral to its upper counterpart, the third premolar. The lower fourth premolar is also rostral to the upper fourth premolar. The upper fourth premolar covers the lower first molar buccally from mesial to distal. The upper first molar may strike the distal occlusal surface of the lower first molar (Fig. 1). Problems associated with feline malocclusions often are due to the development of new breed head types with variable occlusal patterns that fail to conform to normal occlusal relationships. A harmonious correlation between the component parts is of utmost importance for the functional capacity and maintenance of health within the masticatory system. It was believed by early orthodontists that malocclusions in general were diseases of civilization and improper jaw function. With the development of genetic research, malocclusions were found to be the result of inherited dentofacial proportions that are altered by developmental variations, trauma, or altered function. 2 Specific bites or occlusal relationships result from years of established breeding within a family or breed. Although very little has been written about feline dental occlusion, there is now an increasing awareness of the need for treatment of feline malocclusions. Malocclusion results from disproportionate tooth size or from disproportionate length of upper jaw to lower jiJ.W. Small teeth and large jaws, or large maxilla and small mandible, or any combination of these may be inherited. These disproportions in size are rarely seen in the wild, thanks to survival of the fittest. Genetic isolation of species usually produces uniformity in occlusion, with disturbances in occlusion bred out and eliminated from the species. From Colorado State University College of Veterinary Medicine and Biomedical Sciences, Fort Collins, Colorado; and University of Missouri School of Veterinary Medicine, Columbia, Missouri VETERINARY CLINICS OF NORTH AMERICA: SMALL ANIMAL PRACTICE VOLUME 22 • NUMBER 6 • NOVEMBER 1992
1453
1454
EMILY
P3
M1
Figure 1. Normal occlusion.
Malocclusion as primarily a genetic problem was developed by breeding experiments with animals carried out in the 1930s. Experiments by Stockard involved the cross-breeding of dogs.' The results of these experiments apply to feline malocclusion. Stockard crossed dogs of diverse sizes and types to determine the effects on jaw and tooth size. Stockard's experiments indicated that dramatic malocclusions did occur as the result of cross-breeding. These same results are seen in breed type development in cats; for example, discrepancies from tooth size-jaw size imbalances. His experiments concluded that independent inheritance of facial characteristics could be a major cause of malocclusion. The frequency of clinically evident feline malocclusion has been increased by the development of exaggerated head types. With the development of both the brachycephalic and dolichocephalic head types, occlusal relationships and individual teeth can assume positions different from the norm. This is most often expressed in the canine teeth in the extreme brachycephalic breeds, often with craniofacial asymmetry and accompanying wry bite. In the extreme flatnosed brachycephalic types, wry malocclusion is now common. Although teeth other than the canines are often in incorrect position, it is the canine teeth that cause the mechanical effects that present as clinical problems (Figs. 2 and 3). The prevalence of malocclusion in cats has been poorly documented. One study in the United Kingdom reported the prevalence as 3. 9% in all breeds of cats, with an increased prevalence (13%) in the long-haired cats. This study did not specify the prevalence specifically in the brachycephalic and dolicho-
FELINE MALOCCLUSION
1455
Figure 2. Brachycephalic head type. Extraoral canine.
cephalic types. 1 My own subjective observations of the flat-nosed brachycephalic types suggest an approximately 50% incidence of wry malocclusion . It is possible to move teeth by mechanical means into a desired position in many instances. This does not treat the cause of the malocclusion. Such treatment is appropriate only if ethical constraints have been satisfied. ETHICAL CONSIDERATIONS
The continuance of malocclusal problems is largely a result of action by owners of show cats. The short (average 3 to 5 years) life in the show ring is
Figure 3. Brachycephalic head type. Lateral view.
1456
EMILY
often followed by years of breeding for cats that have achieved high status in the show ring. In that time, many types of malocclusion could be transmitted genetically. Ethical treatment of both genetic and developmental problems in cats is greatly influenced by cat breed standards. Dental standards are somewhat different for feline dentition and bite relationships than in dogs. Strict limitations regarding dental treatment are rigidly mandated by the American Kennel Club. They rightly state that dogs to be exhibited in the show ring cannot have a dental fault disguised by orthodontics or cosmetics to improve o~ normalize the dog's appearance. Such a specimen could transfer the fault to their offspring, degrading the breed. Feline show regulations do not stress bite types as a fault or disqualification, only that teeth should not be visible when the mouth is closed. Modern feline show' breeding has followed two trends, by exaggeration of the normal feline maxillary/mandibular relationship . In the brachycephalic breeds, the micrognathic maxilla has reduced arch space with crowding of the dentition, often with the superimposed cranial asymmetry of wry malocclusion. Unilateral mandibular prognathism is a common complication; one lower canine is visible because it sits outside the lip when the mouth is closed. This often results in soft tissue trauma to the upper lip (see Figs. 2 and 3). The dolichocephalic types frequently present with upper or lower canine teeth tipped laterally (buccal version), again producing soft tissue trauma (Fig. 4). Ethical considerations should stress protection of the proper occlusal relationship through sound breeding principles. Disregard of sound breeding can result only in perpetuation of unfit specimens. It is the duty of the veterinarian, however, to provide for a trauma-free and comfortable occlusion; cats with malocclusions that are to be treated orthodontically should be neutered.
Figure 4. Dolichocephalic head type. Lateral view.
FELINE MALOCCLUSION
1457
TREATMENT Feline orthodontic problems are often difficult to correct mechanically. The small shallow confines of the mouth make placement of bands, arch wires, and ligatures difficult. The short straight-sided premolars and tight shearing action of the carnassials present additional problems for proper band and bracket placement. Because feline show regulations require only that the teeth are not visible when the mouth is closed, the most practical, successful, and trauma-free therapy for those teeth creating soft tissue trauma is extraction or coronal length reduction and vital pulpotomy (see the article on endodontics for pulpotomy procedure elsewhere in this issue). Vital pulpotomy takes the offending teeth out of contact with the soft tissue while maintaining tooth vitality. Mechanical movement of feline dentition is rarely needed for function. It is difficult to perfect, is traumatic, and is subject to repeated failure. Mechanical movement of prognathic extraoral mandibular canine teeth in labial version may be accomplished in the rare case in which there is need for it. Many types of tooth movement can be used . A simple cost-effective procedure uses hand-fashioned light ligature wire hooks secured to the labial surface of the canines with light bonded composite cement. The hooks are fashioned from 26-gauge wire using fine beak orthodontic pliers . For canine teeth that sit outside the lip when the mouth is closed (as seen in the wry malocclusions), a similar hook is secured to the lingual surface of the opposite lower first molar tooth because these canines usually need to be tipped lingually as well as distally. Buttons or hooks cannot be placed on the buccal surfaces of the lower first molar owing to the shearing action of the opposing upper fourth premolar against the buccal surface of the lower first molar. A light rubber ligature or power chain is placed between the canine and molar hooks. The cat usually tolerates the displacement of the tongue by the elastics or power chain fairly well (Fig. 5). Canine teeth in labial version as seen in the dolichocephalic breeds are moved similarly except the caudal hook is placed on the lingual surface of the
Figure 5. Wry malocclusion: Rubber power chain from extraoral canine to medial, lower, opposite first molar.
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A
Figure 6. A, Drawing, and 8, clinical view of labial prolusion of upper and lower canines. Rubber power chain from buccal to lingual lower; buccal to buccal upper.
Figure 7. Mandibular displacement resulting from poor fracture reduction .
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Figure 8. Vital pulpotomies to correct soft-tissue trauma shown in Figure 7.
lower first molar on the same side. For the upper canine tooth, the caudal button or hook is light-bonded to the buccal surfaces of the upper fourth premolar and the upper canine (Fig. 6). Obviously proper breeding principles are the ultimate corrective measures. Simple relief of soft tissue trauma through extraction or vital pulpotomy is the most ethical and practical therapy.
ACQUIRED MALOCCLUSION
Acquired malocclusion in cats is usually due to trauma or disease rather than produced by habitual behavior, as seen in humans. Trauma to developing permanent tooth buds, drift of permanent teeth owing to premature loss of primary teeth, and trauma to permanent teeth can lead to malocclusion. Primary teeth retained past their normal time of exfoliation, however, is not a common finding in cats. Traumatically induced malocclusion is usually the result of poor mandibular fracture reduction. This can result in mild to radical mandibular displacement with soft tissue damage produced by teeth out of alignment (Fig. 7). These teeth are best treated with vital pulpotomy to relieve tissue damage (Fig. 8). Mandibular symphyseal fractures are the most common type of fracture in cats and are comparatively easy to reduce; however, mandibular body fractures will result in malocclusion if improperly reduced. Temporomandibular joint fractures require special reduction or surgical intervention to avoid malocclusion. Mandibular luxation is usually the result of trauma, but genetically weak temporomandibular ligaments or attachments can cause subluxation and resulting malocclusion. Electric cord injury with gingival and osseous necrosis with tooth displacement can produce malocclusion. . Mass lesions either benign or neoplastic can result in malocclusion by mass displacement of the dentition.
1460
EMILY
References 1. Crossley DA: J Br Vet Assn 1991 2. Proffit WR: Contemporary Orthodontics. St Louis, CV Mosby, 1989 3. Stockard CR: The genetic and endocrine basis for differences in form and behavior as elucidated by studies of contrasted pure-line dog breeds and hybrids. American Anatomical Memoirs. Philadelphia, Wistar Institute, 1941
Address reprint requests to Peter Emily, DDS 1051 Independence Street Lakewood, CO 80215
